Five-year multicenter retrospective review of cyclobenzaprine toxicity

Cyclobenzaprine (CBP) has a cyclic structure similar to amitriptyline. In overdose, CBP has been suggested to produce the cardiovascular and neurologic toxicity found with the cyclic antidepressants. To examine this possibility, a retrospective chart review of all cases of CBP exposure reported to five regional poison centers was performed for the years 1989-93. There were a total of 750 charts identified for CBP exposure, of which 523 had data sufficient for evaluation. There were 121 polydrug ingestions leaving 402 pure CBP ingestions. Ages ranged from 7 mo to 77 yrs, with a mean of 20 yrs; 26% were 6 yrs or less. Females comprised 63% of the patient group. No deaths occurred. Dysrhythmias beyond sinus tachycardia were infrequent, and none were life-threatening. No seizures occurred. Common effects were lethargy, sinus tachycardia, and agitation, and both hypertension and hypotension were seen. All symptomatic cases with a known time of ingestion were symptomatic within 4 h of ingestion. Doses ingested ranged from 5-1000 mg, with a mean of 133 mg. Asymptomatic and symptomatic patients had a mean dose ingested of 45 mg and 183 mg, respectively. Treatment was primarily gastrointestinal (GI) decontamination and supportive care. Other therapies required were mechanical ventilation, dopamine, fluid bolus, sedation, and foley catheter. Symptoms requiring treatment beyond GI decontamination did not occur with ingestions less than 100 mg. In conclusion, cyclobenzaprine does not appear to produce the life-threatening cardiovascular or neurologic effects of the cyclic antidepressants in doses less than 1 g. Lethargy and anticholinergic effects are prominent, though serious toxicity is infrequent.     

Human sulfite oxidase R160Q: identification of the mutation in a sulfite oxidase-deficient patient and expression and characterization of the mutant enzyme

Sulfite oxidase catalyzes the terminal reaction in the degradation of sulfur amino acids. Genetic deficiency of sulfite oxidase results in neurological abnormalities and often leads to death at an early age. The mutation in the sulfite oxidase gene responsible for sulfite oxidase deficiency in a 5-year-old girl was identified by sequence analysis of cDNA obtained from fibroblast mRNA to be a guanine to adenine transition at nucleotide 479 resulting in the amino acid substitution of Arg-160 to Gln. Recombinant protein containing the R160Q mutation was expressed in Escherichia coli, purified, and characterized. The mutant protein contained its full complement of molybdenum and heme, but exhibited 2% of native activity under standard assay conditions. Absorption spectroscopy of the isolated molybdenum domains of native sulfite oxidase and of the R160Q mutant showed significant differences in the 480- and 350-nm absorption bands, suggestive of altered geometry at the molybdenum center. Kinetic analysis of the R160Q protein showed an increase in Km for sulfite combined with a decrease in kcat resulting in a decrease of nearly 1,000-fold in the apparent second-order rate constant kcat/Km. Kinetic parameters for the in vitro generated R160K mutant were found to be intermediate in value between those of the native protein and the R160Q mutant. Native sulfite oxidase was rapidly inactivated by phenylglyoxal, yielding a modified protein with kinetic parameters mimicking those of the R160Q mutant. It is proposed that Arg-160 attracts the anionic substrate sulfite to the binding site near the molybdenum.